It is possible to be for example against US influence in Syria and against Assad the same time, you know?
Of course, but pretty much nobody who uses terms like "tankie" acknowledges that in practice.
When I say that I oppose US intervention in, say, North Korea, then I'm immediately hit with all kinds of horror stories about how everyone has to get the same haircut or whatever. If I refute that misinformation and insist that I don't want the US to overthrow their government, then I will inevitably be accused of "defending North Korea," labelled as a "tankie" and then subject to the whole rumor mill about "what tankies believe" that's completely detached from reality or anything I actually say or believe. Next thing you know, I'm being accused of wanting every country in the world to become like North Korea. If I deny that, then it's assumed that I'm just concealing my "real" views.
It's the same way in every conflict in history since the dawn of time. When I was 10 years old asking why we didn't respond to 9/11 by "turning the other cheek" like I'd been taught, people looked at me like I was some kind of "terrorist sympathizer" because "you're either with us or against us." Every single time I have opposed any conflict, I have been accused of "supporting" or "defending" the other side, regardless of what I actually say or what reasons I actually provide.
There's no use trying to fight it. Instead of trying to, and looking like I'm trying to weasel out of the label like I have something to hide, I'd rather just accept it so that I have some ability to speak for what us "tankies" actually believe. Starting with, opposition to building more tanks. Opposition to building tanks is the defining characteristics of a "tankie" because if you don't want to build and deploy tanks then you're assumed to "support" whatever enemy-of-the-week they're to be used against, who is no doubt "authoritarian." Likewise, anti-militarism will cause me to be labelled as a "campist" for "supporting" the target of that militarism. When you're being accused of such things, nobody gives a shit about the nuance between "supporting" or "opposing action against," and even if you insist on it they'll just say you're lying and that you actually do support the "bad guy."